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Full Discussion: How to check if process is running?
Special Forums UNIX and Linux Applications How to check if process is running? Post 302417072 by Corona688 on Wednesday 28th of April 2010 12:01:33 PM
Old 04-28-2010
A traditional way is for a process to create a PID file under /var/run/. I create it under /tmp/ just as an example that can run as any user. I also use a fifo as a lock file to prevent a race condition.

Code:
#!/bin/bash

function rm_pidfile
{
        rm -f /tmp/myscript.pid
}

function is_running
{
        # File does not exist, we can run
        [ -f /tmp/myscript.pid ] || return 1
        # Read PID from file
        read PID < /tmp/myscript.pid
        # File exists but process does not.
        [ -d /proc/${PID} ] || return 1
        return 0
}

# This guarantees other scripts will wait for each other
# before checking the pidfile.  otherwise one might create the PID
# file while we're not looking.
while ! mkfifo /tmp/myscript.lock 2> /dev/null
do
        sleep 1
done

# beyond this point, /tmp/myscript.lock exists and belongs to us.  Other
# instances of the script will loop.

if is_running
then
        echo "An instance(PID ${PID}) is already running"
        rm -f /tmp/myscript.lock
        exit 1
fi

# create PID file
echo "$$" > /tmp/myscript.pid

# make sure we delete it when the program quits
trap "rm_pidfile" EXIT

# Remove the lock file
rm -f /tmp/myscript.lock

# the rest of the code goes here

while true
do
        sleep 1
done

 

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LEARN ABOUT PHP

com_get_active_object

COM_GET_ACTIVE_OBJECT(3)						 1						  COM_GET_ACTIVE_OBJECT(3)

com_get_active_object - Returns a handle to an already running instance of a COM object

SYNOPSIS

       variant com_get_active_object (string  $progid, [int  $code_page])

DESCRIPTION

       com_get_active_object(3)  is similar to creating a new instance of a "COM" object, except that it will only return an object to your script
       if the object is already running. OLE applications use something known as the " Running Object Table" to allow well-known  applications	to
       be launched only once; this function exposes the COM library function GetActiveObject() to get a handle on a running instance.

PARAMETERS

	      o $progid
		-$progid must be either the ProgID or CLSID for the object that you want to access (for example Word.Application).

	      o $code_page
		- Acts in precisely the same way that it does for the "COM" class.

RETURN VALUES

	If the requested object is running, it will be returned to your script just like any other COM object.

ERRORS
/EXCEPTIONS
	There  are a variety of reasons why this function might fail, the most common being that the object is not already running. In that situa-
       tion, the exception error code will be MK_E_UNAVAILABLE; you can use the getCode method of the exception  object  to  check  the  exception
       code.

NOTES

       Warning

	       Using  com_get_active_object(3)	in  a web server context is not always a smart idea. Most COM/OLE applications are not designed to
	      handle more than one client concurrently, even (or especially!) Microsoft Office. You should read Considerations for Server-Side Au-
	      tomation of Office for more information on the general issues involved.

PHP Documentation Group 												  COM_GET_ACTIVE_OBJECT(3)
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